Sewage Treatment Plants

Innovative water management. Eco friendly results

The sewage treatment process relies on the action of bacteria, which are naturally present in sewage, to consume the waste matter and break it down. The bacteria need food and oxygen to survive, and they naturally colonise any areas which provide these elements.

Package treatment plants come in three basic designs:

Type 1

The first type relies upon a plastic media filter bed through which liquid sewage is trickled. The filter bed is home to millions of naturally occurring bacteria which feed on the nutrients in the sewage. Air rises through the filter bed by natural convection to provide oxygen for the bacteria. The partially treated liquid is collected in a separate tank beneath the bed, and pumped back to the top of the plastic media to repeat its treatment. The process is the same as can be seen at a sewage works where wastewater is sprayed onto a circular bed of clinker.

Type 2

The second is the S.A.M unit. This is short for Submerged Aerated Media. The plant comprises a tank filled with pieces of plastic (the media) to which bacteria adhere. The plastic is then submerged in liquid sewage which provides the food element for the bacteria. The oxygen for the bacteria is provided by an air blower or compressor blowing bubbles through the liquid sewage. By this method the bacteria are in permanent contact with the sewage, so have a constant supply of food.

Type 3

The third type of sewage plant is the “ Rotating Biological Contractor” or more simply an “R.B.C” The Klargester R.B.C (biodisc) is effectively a five star, all inclusive hotel for friendly bacteria. Sewage entering the Klargester passes through three stages. Its treatment process combines the advantages of the other two types of plant. The first stage is a tank which separates solid matter and retains it as inert sludge, to be removed by vacuum tanker.

The second stage treats the liquid sewage and consists of packs of slowly revolving discs, which are “home” for the bacteria. The discs are half submerged in liquid sewage, so the bacteria alternately “breathe” and “feed” on every revolution. The Klargester unit only allows a measured amount of liquid sewage into the bacteria zone at each revolution. This ensures that all the sewage receives treatment. No other machine uses this “managed flow” principle. After the bacterial treatment, the liquid is passed into a final tank where it is retained long enough to allow any remaining suspended particles to sink to the bottom before it is discharged as clear water into a ditch or surface watercourse.

Overall, the final treated effluent from these units generally complies with the purity requirements of the Environment Agency, but it is essential to note the building regulations require that any new unit purchased must carry a CE mark otherwise it will be rejected by the building control officer.